1. Field of the Invention
The present invention relates to a method of using a large screen low-density dot-matrix display device to display high-density bit-mapped dot-matrix image data. Specifically, the present invention relates to a method of obtaining as fine an image as possible through the aforesaid large screen dot-matrix display.
2. Description of the Related Art
Large-scale dot-matrix displays of the type consisting of an array of vertically and horizontally oriented rows of light emitting diodes are frequently used on buildings, in sports stadiums, and at other locations as a means of imparting information visually. These types of displays use large display surfaces which generally offer a similar image resolution to that of conventional television.
A typical television receiver offers a level of image resolution equivalent to 480 vertical and 720 horizontal display lines. Bit mapped image data applied to this resolution standard is processed as 480 vertical dots by 720 horizontal dots. If this data display standard were to be applied to a large screen dot-matrix display having, for example, a 96 vertical by 144 horizontal dot pattern, the result would be a display that offers only one fifth of the resolution that the bit-mapped image data is capable of.
The simplest way to execute control of this type of display is to thin out the horizontal and vertical dot density to one fifth normal density whereby the 480 by 720 bit-mapped image data is re-formatted into the 96 by 144 pattern, and to drive each dot in the 96 by 144 dot pattern with one bit of data. Through this method, only one dot of image data is used to drive one dot of display within an area in which 25 dots (5×5) of image data are available.
A significant amount of data is lost and image resolution lowered as a result of this image thinning display control method. Furthermore, when only this thinning process is applied, an aliasing effect is generated which significantly lowers image quality. It is known in the art that image format conversion, a process in which image data within a very small image area is averaged, can be applied to reduce the adverse affects of aliasing. Aliasing can be reduced, for example, through the averaging conversion offered by a low-pass filter in which one dot of image data is averaged from twenty five (25) dots (5×5), or from nine (9) dots (3×3) within the 5×5 dot area (in this case, sixteen (16) dots of data (25-9) are ignored). After this format conversion is executed, that one dot of averaged image data is used to drive one display dot on screen. It is also known in the art that a weighted averaging format conversion operation can be applied in which the central portion of a small group of dots is specifically stressed, or “weighted” in the data conversion process. Bilinear, cubic spline, and Gaussian filters are some examples of weighted averaging format conversion.
Low-density bit-mapped image data can be derived from high-density image data through an averaging format conversion process and displayed on a large-scale low-density dot-matrix display device. Once the required control parameters are set, this method results in improved image quality when compared to simple image thinning.
With respect to a structure of display devices, it is advantageous to employ a low-density dot-matrix device for the above high-density image display since recent examples of large-scale display systems generally include a relatively thick and solid panel structure, in which a number of light emitting elements such as a high-intensity LED combination lump. Because of electronic devices for driving the elements installed in the panel structure, the panel structure cannot be transparent. However, in today's planning and designing of buildings with various types of facades such as a curtain wall, there arise needs for a large-scale display device capable of maintaining visibility through the display device as well as the facade. Obviously, the above conventional display device with a solid panel structure cannot be employed for this use.